A contemplated application of the present invention is in an ion implanter that may be used in the manufacture of semiconductor devices or other materials. In such an application, semiconductor wafers are modified by implanting atoms of desired species into the body of the wafer, for example to form regions of varying conductivity.
Ion implanters are well known and generally conform to a common design as follows. An ion source generally comprises an arc chamber in which a plasma is generated. The plasma will contain ions of a desired species to be implanted. The conditions under which the ion source operates affects the plasma produced. For example, varying the operational parameters affecting the ion source may change the number of ions in the plasma, the composition of the ions in the plasma (e.g. by promoting cracking of molecules), and the energy of ions in the plasma.
An extraction lens assembly produces an electric field that extracts ions from the ion source and forms a mixed beam of ions. Only ions of a particular species are usually required for implantation in a wafer or other substrate, for example a particular dopant for implantation in a semiconductor wafer. The required ions are selected from the mixed ion beam using a mass-analysing magnet in association with a mass-resolving slit. By setting appropriate operational parameters on the mass-analysing magnet and the ion optics associated therewith, an ion beam containing almost exclusively the required ion species emerges from the mass-resolving slit.
This ion beam is transported to a process chamber where the ion beam is incident on a substrate held in place in the ion beam path by a substrate holder. The ions may be accelerated or decelerated and focused prior to implantation. Other ion optics may be included along the ion beam path to steer and shape the ion beam, and prevent loss of ion current from the ion beam.
The various parts are operated under the management of a controller, typically a suitably-programmed personal computer or the like. A more detailed description of an ion implanter can be found in U.S. Pat. No. 4,754,200.
Accordingly, there are many operational parameters associated with the ion implanter that influence the ion beam that reaches the wafer. In particular, control of these parameters is required to ensure a desired ion beam current, energy, size and shape. Moreover, any of these ion beam attributes may vary from implant recipe to implant recipe.